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Disturbances are one of the most important processes affecting natural systems, but there is a gap between the simplicity of conceptual models of disturbance and the rich complexity of empirical studies. We studied the perturbation caused by the movement of headward-eroding creeks onto the marsh platform in southeastern USA salt marshes. We measured the disturbance responses of 19 variables in terms of both magnitude (the difference between perturbed areas and control areas located on the marsh platform) and recovery trajectory (evaluated using a space for time substitution design along a marsh transect that ran the length of the newly-formed creek). Some variables (shoot density, root biomass, herbivorous snail density, soil pH, soil strength, soil temperature and elevation) declined sharply, while other variables (crab burrow density, soil organic matter and soil redox) increased sharply, in response to the heavily burrowed and grazed conditions at the creek head; these then recovered over subsequent years or decades. Other variables (shoot height, aboveground biomass, rhizome biomass, and light interception) declined sharply in the creek head, then overshot control values before recovering. Some variables (benthic algae, soil salinity) did not appear to be disturbed by the creek head. As hypothesized, plants recovered before soils and before snails. Disturbance magnitude and time to recovery were often greater directly adjacent to the new creekbank than for the same variables in a parallel transect further away from the creekbank that experienced an initial perturbation at the creek head but was not subject to the ongoing influence of the newly-formed creek, and in some cases variables never recovered, indicating a state change. Reducing the dimensionality of the data set into one or two principal component axes obscured the diverse ways in which different aspects of the system responded to and recovered from the perturbation. Our study illustrates the challenges in moving from simple conceptual models of disturbance to empirical studies in which multiple variables are likely to be affected differently and follow different recovery trajectories.

Wu, F., Pennings, S.C., Ortals, C., Ruiz, J., Farrell, W.R., McNichol, S.M., Angelini, C., Spivak, A.C., Alber, M. and Tong, C. 2021. Disturbance is complicated: headward-eroding saltmarsh creeks produce multiple responses and recovery trajectories. Limnology & Oceanography. 67:S86-S100. (DOI: 10.1002/lno.11867)